Collapsible revolving door having pairs of pivot detents at the top and bottom of each leaf

ABSTRACT

A collapsible revolving door with upper and lower mechanisms which enable the folding of the revolving door leaves upon the application of a predetermined abnormal pressure thereto. A mechanism includes a retaining plate concentrically mounted on the end of the central vertical door shaft; horizontal bearing plates mounted on the horizontal edge of each door leaf adjacent to the central shaft; and a pair of detents connecting each bearing plate to its associated retaining plate, one detent on either side of the door leaf axis. Upon application of an abnormal force, the upper and lower detents on one side of the door leaf yield allowing the door leaf to pivot about the detents on the other side of the leaf enabling folding.

United States Patent [19] Lowe 'IIlIllI' .uunu

Jan. 1, 1974 [57] ABSTRACT A collapsible revolving door with upper andlower mechanisms which enable the folding of the revolving door leavesupon the application of a predetermined abnormal pressure thereto. Amechanism includes a retaining plate concentrically mounted on the endof the central vertical door shaft; horizontal bearing plates mounted onthe horizontal edge of each door leaf adjacent to the central shaft; anda pair of detents connecting each bearing plate to its associatedretaining plate, one detent on either side of the door leaf axis. Uponapplication of an abnormal force, the upper and lower detents on oneside of the door leaf yield allowing the door leaf to pivot about thedetents on the other side of the leaf enabling folding.

9 Claims, 15 Drawing Figures Illlllll lllll r PAIENTEDJAVN H I 3.782.035

I SNEU 2 (If 4 1 COLLAPSIBLE REVOLVING DOOR HAVING PAIRS OF PIVOTDETENTS AT THE TOP AND BOTTOM OF EACH LEAF The invention relates to arevolving door of the type having a central vertical rotating shaft anddoor leaves normally rotating with and extending from the central shaftalong radial door axes. More specifically, the invention relates to arevolving door in which the leaves are adapted to fold under abnormalpressure so as to create an open passage through the doorway. Revolvingdoors of this type are often referred to as collapsible revolving doors.

Many different types of collapsible revolving doors have been built inthe past which incorporate mechanisms to retain the door leaves normallyin their extendedposition and to guide the leaves to theircollapsedposition. These mechanisms are usually quite complicated andare exposed to view creating an unsightly appearance for the door. InUS. Pat. No. 2,495,251 which issued Feb. 10, 1970 to Dennis Lowe thereis disclosed a collapsible revolving door in which the mechanism isconcealed, but this mechanism is relatively expensive to manufacture.

It is therefore an object of the present invention to provide a simpleinexpensive collapsing mechanism which is also substantiallyentirelyconcealed. In a typical embodiment the mechanism includescircular retaining plates concentrically mounted, one at the top and oneat the bottom of the central vertical shaft of the door. These retainingplates extend radially outwardly beyond the inner corners of the doorleaves. Horizontal bearing plates are mounted on the top and bottomedges of each of the door leaves adjacent to the central shaft andbetween said door leaf edges and their associated retaining plates.

Between each bearing plate and its associated retaining plate a pair ofdetents is connected. The detents are located on opposite sides of theplane of the door leaf and adjacent to the central vertical shaft. Whenan abnormal pressure is exerted on a door leaf, the top and bottomdetents on one side of the leaf yield and release allowing the door leafto pivot about the top and bottom detents on the other side of the leaf,thus enabling folding.

Further objects and advantages of the invention will appear from thefollowing disclosure, taken together with the accompanying drawings inwhich:

FIG. 1 is a perspective view of a typical revolving door according tothe invention,

FIG. 2 is a perspective view of a retaining plate for the FIG. 1 door;

FIG. 3 is a perspective view of a bearing plate for the FIG. 1 door;

FIG. 4 is an oblique sectional view of a detent for the FIG. 1 door;

Reference is first made to FIG. 1 which shows in perspective a typicalrevolving door 2 according to the present invention, revolving in ashell 3. The door 2 includes four leaves 4 mounted to rotate with acentral vertical shaft 6 normally hidden from view by a weather barrier8. The tops of the leaves 4 and the central shaft 6 are connected to anupper collapsing mechanism 10 partially recessed in the ceiling 12,while the bottoms of the leaves 4 and central shaft 6 are similarlyconnected by a lower collapsing mechanism 14 partially recessed in thefloor 16. The mechanisms 10, 14 maintain the door leaves in a radiallyextended position as shown while permitting rotation of the leaves andcentral shaft about the central vertical axis of the door, and themechanisms 10, 14 also control the collapse of the leaves, as will bedescribed.

The upper and lower collapsing mechanisms 10, 14 are normally identical,although minor differences (to be described) may be incorporated ifdesired. Primed reference numerals in the drawings will be used toindicate parts in the upper collapsing mechanism 10 corresponding tothose in the lower collapsing mechanism 14.

Reference is next made to FIGS. 2 to 7 which show the components of apreferred embodiment of the lower collapsing mechanism 14. FIG. 2 showsa typical retaining plate 18 for the collapsing mechanism 14. Theretaining plate 18 includes a central sleeve 20, a central aperture 22for the central vertical shaft 6, and an outer disc portion 24 typicallycast integrally with the sleeve 20.

The disc portion 24 includes eight holes 26, two for each door leaf 4.The two holes 26 associated with each door leaf 4 are located onopposite sides of the plane of their respective door leaf in such amanner that the door leaf 4 is permitted to collapse, as will bedescribed. Each of the holes 26 includes a circumferential ledge 27which seats one of the detents (ball holders to be described) formingpart of the mechanism for maintaining the door leaves in a radiallyextended position.

Reference is next made to FIG. 3 which shows a typical bearing plate 28for the collapsing mechanism 14. One bearing plate 28 is mounted on thebottom edge of each door leaf4 at a position adjacent to the centralvertical shaft 6 (as shown in FIG. 8 and in FIGS. 10 to 13). Thus thereare four bearing plates for the lower portion of the door. (Similarlythere are four bearing plates 28' for the upper collapsing mechanism,one mounted on the upper edge of each door leaf in a position adjacentthe central shaft 6, as shown in FIG. 8.)

Each bearing plate 28 includes (see FIG. 3) a central arcuate edge 30and an outside arcuate edge 32. When the four bearing plates are inposition at the upper or lower portion of the door the arcuate edges 30form a hole to accommodate the central vertical shaft 6.

Two bearing plate holes 34 are drilled part way into the bearing plate28 on opposite sides of the door leaf plane, in positions which match apair of retaining plate holes 26 when the bearing plate is placed overthe retaining plate. The two holes 34 accommodate detent members to bedescribed. The bearing plate 28 also includes a screw hole 35 toaccommodate a screw for fastening the bearing plate to a door leaf, aswill be described.

Reference is next made to FIG. 4 which shows a preferred embodiment of adetent, namely a ball socket 36 which fits into the holes 26 in theretaining plate 18.

Socket 36 includes a spherical ball 38 retained inside a tubular housing40. The upper end of the tubular housing 40 includes a rounded inneredge 42 which retains the ball 38 (typically stainless steel 1 inch indiameter) in a position projecting from the socket. The upper end ofhousing 40 also includes an outer shoul' der 44 which seats on the ledge27 when a ball socket 36 is mounted in a retaining plate hole 26, toprevent the socket 36 from being pushed through hole 26 when pressure isapplied to ball 38.

A heavy coil spring 46 inside the tubular housing 40 urges the balloutwardly to its extended position. A plug 48 is inserted into thebottom of tubular housing 40 to hold coil spring 46 in place. The plug48 may be secured in any desired manner (e.g. welded) or it may bethreaded into the end of the tubular housing 40 to allow adjustment ofthe compression of coil spring 46 and replacement of the parts.

Reference is next made to FIGS. 5, 6 and 7, which show at 50 inorthographic projection a detent (a ball socket) which fits into theholes 34 in the bearing plates 28. The ball socket 50 includes a shallowrecess 52, of spherical curvature, which accommodates the detent ball38. The recess 52 is bounded by and set into a generally conicalshoulder 54. A flat surface 56 is produced on one side of the conicalshoulder 54 to form a run-out from recess 52 so that the spherical ball38 may be removed horizontally from recess 52 in one direction (namelyover the run-out 56) with very little force. However, a very substantialforce is required to remove the ball from the recess in any otherhorizontal direction. This characteristic is due to the fact that thedetent ball 38 is only required to be depressed slightly to move it inthe direction of the run-out 56 (since shoulder 54 is quite low atrun-out 56) while a much higher depression is required to move the ball38 in any other direction.

The detent or ball socket 50 also includes a cylindrical base 58 whichfits into one of the bearing plate holes 34 to hold the ball socket inposition.

It will be appreciated that instead of providing a separate and discreteball socket 50, the recess 52 and the run-out 56 could be cut into thebearing plate 28 in place of each hole 34. However, by casting the ballsockets 50, which is a very simple operation, a less expensive assemblyresults and the ball sockets are easily replaceable.

Reference is next made to FIG. 8 which shows how the central verticalshaft 6, the upper and lower collapsing mechanisms 10, 14, and theirassociated parts are mounted on the floor and ceiling and connected todoor leaves 4. The lower portion of the door will first be described. Asdiscussed previously, the lower portion is identical to the upperportion of the door.

The lower collapsing mechanism 14 is supported in a cylindrical housing60. Housing 60 is located in a well in the floor 16 and includes acylindrical sleeve 62 therein which supports a thrust bearing 64. Thrustbearing 64 in turn supports and aligns the bottom of the door bysupporting the retaining plate 18. The retaining plate 18 is secured bywelding or by a pin, not shown, to the lower end of the central shaft 6with the central sleeve 20 facing away from the door leaves 4.

A similar support arrangement is used, as shown, at the top of the door,but the upper support housing 60 is fixed to heavy structural members 65in the ceiling 12. The portion of the ceiling 12 normally visible toviewers is indicated in FIG. 8 at 650 and is typically made of plywoodheld to structural members 65 by supports 65b, employing adhesive orscrews (not shown).

Referring again to the bottom of the door, eight ball holders 36 aremounted in the eight retaining plate holes 26 so that the detent balls38 face the door leaves 4. A sealing ring 66 is set in the floor 16 toprevent dirt from falling through the space between the support housing60 and the retaining plate 18. No sealing ring is needed at the top ofthe door.

The bearing plates 28 are mounted on the door leaves 4 as follows. Eachdoor leaf comprises conventional frame members 67, welded or screwedtogether, which encircle and retain the glass 68 of the leaf. A U-shaped stainless steel member 69 extends for a short distance along thebottom and top of each door leaf and also extends along the innervertical edge of the door leaf, and is secured to the leaf by a numberof screws 69a spaced along the length of member 69. The bearing plates28 are welded to the rspective members 69 so that there is a bearingplate 28 or 28 oriented horizontally at the bottom and top inner cornerof each door leaf, as shown. The screws 69a help to secure the bearingplates to their respective U-shaped members 69. This arrangementprovides a secure connection between the bearing plates and the doorleaves.

The ball sockets 50 are press-fitted or otherwise secured in the bearingplate holes 34 so that the run-outs 56 are in a direction parallel tothe door leaf axis and facing the central shaft 6, as shown. Thus it canbe seen that the ball holders 36 and the ball sockets 50 connect thebearing plates 28 (and hence the door leaves) with the retaining plate18 (and hence the central shaft 6). In fact, this is the only connectionbetween the door leaves 4 and the central shaft 6. Also, the weight ofeach door leaf 4 is transmitted through the bearing plates 28, the ballsockets 50, and the ball holders 36 to the retaining plate 18 andfinally to the thrust bearing 64. Thus, the door leaves 4 are directlysupported for rotation with the central shaft and held in a radiallyextended position by the operation of the ball holders 36 and ballsockets 50. It is these two elements which also enable the door leaves 4to be folded as will be described.

The central shaft 6 extends vertically from the retaining plate 18 andis formed in two sections, namely a lower section 6a and an uppersection 6b (see also FIG. 8A). A reduced diameter post 71 projectsupwardly from the top of the lower shaft portion 6a, the post 71 havingan exterior thread 72. Another reduced diameter post 73 is secured toand projects downwardly from the upper shaft portion 6b. The post 73carries a slightly enlarged end plate 74 from which a flattened locatingpiece 75 projects downwardly (see also FIG. 9). The locating piece 75 isadapted to fit into a locating slot 76 (FIG. 8B) in the top of the post71. A nut 77 is slidably mounted on the post 73 so that it can slide upand down over the plate 74. The nut 77 carries an interior thread 78 sothat it can be screwed onto the threaded post 71.

The shaft 6 is installed by placing the lower portion 6a, with itsretaining plate 18 and ball holders, in position in the bearing 64, andby placing the upper portion 6b, with its retaining plate 18 and ballholders, in the upper bearing 64'. (The ball holders 36 are retained intheir retaining plate 18' by friction at this time.) The upper and lowershaft portions may each be tilted slightly in a shallow V-configurationat this time, to allow installation of both portions. The locating piece75 is then slid into the slot 76. Once the piece 75 is located in theslot 76, the shaft portions 6a, 6b are straight with respect to eachother. The upper bearing 64' can move slightly upwardly at this timebecause its socket 64a is longer than the bearing 64'.

Next, the nut 77 is pulled down over the post 71 and partly, but notfully, tightened. After this has been done, each door leaf 4 isinstalled in the book folded position shown (and later described) inFIG.13. This is accomplished by setting the run-outs 56 of the ball sockets50 at one side of the top and bottom of each leaf against the detentballs 38 and then pushing the leaves radially inwardly towards centralshaft 6.

With the leaves installed in the book folded position, the nut 77 istightened all the way, moving the lower and upper retaining plates 18,18 slightly together and compressing" the leaves 4 between them(actually .the springs 46 are compressed as the retaining plates 18, 18'move towards each other).

After the shaft and leaves are installed, the weather barrier 8 isplaced around the shaft 6. The weather barrier 8 (see FIG. 9) istypically formed as two aluminum extruded halves 80, 82 which arefastened to the central shaft by any desired means, e.g. by screws.(When the leaves are book folded, half of the central shaft isaccessible to attach half of weather barrier 8, and then the leaves maybe book folded the other way to attach the other half of weather barrier8.)

The inner edges of the leaves may be provided with weather stripping 86,secured between member 69 and the door leaf frame 67, to seal the spacebetween the inner edges of the door leaves 4 and the central shaft 6. Noidentations are needed in the weather barrier 8 to allow for folding ofthe leaves, because the leaves swing substantially out when they arefolded, as will now be described.

Reference is next made to FIGS. 10 to 13 which show the operation of thedoor by illustrating various positions assumed by the leaves 4 and thebearing plates 28 as folding progresses. In FIGS. 10 to 13, the fourdoor leaves 4, four bearing plates 28, and four pairs of ball holders 36are distinguished one from the other by the suffixes a, b, c, and d.

Referring to FIG. 10, assume that an abnormal force F is being appliedto the door in the direction of the arrows. This abnormal force mayoccur when people are streaming toward the door in a panic situation, orwhen it is desired to fold the door leaves for special purposes.

When the force F contacts the two leading door leaves 4a, 4b thepressure on these leaves is transmitted through the bearing plates 28a,28b and the ball sockets 50 to the ball holders 36 which are supportingthe door leaves 4 and holding them in position. (As discussed the detentmechanism for each door leaf is constituted by springs 46 pressing theballs 38 vertically into the ball sockets 50.)

The force F tends to cause the door leaf to rotate and move the bearingplates and ball sockets horizontally. This horizontal motion isconverted into a vertical force and motion by the action of the ballsocket spherical recess 52 on the detent ball 38. The ball 38 is forcedto move vertically downwardly into the detent housing 40.

As was discussed, the run-outs 56 on the ball sockets 50 are aligned ina direction parallel to the door leaves 4 and facing the central shaft6. Also, a relatively low force is required to move a detent ball 38situated in the spherical recess 52 horizontally in the direction of therun-out 56, and a very high force is required to move a detent ball 38in the opposite direction.

Consider first the detent on the side of door leaf 4a nearest the forceF. Bearing plate 28a tends to rotate counter-clockwise. This motioncauses the right hand (as drawn) ball socket 50 of plate 28a to movehorizontally away from central shaft 6. Only a relatively small forceand depression of the detent ball 38 of the right hand ball socket 50 isrequired to release it from the ball socket allowing the bearing plateto continue rotating counter-clockwise.

Consider next the detent on the side of door leaf 4a farthest from forceF. The rotating tendency of bearing plate 28a tends to cause the lefthand ball socket 50 to move horizontally toward central shaft 6. Sincerunout 56 is also in the direction of shaft 6, a very high force andlarge depression of ball 38 is required to release ball 38 from the ballsocket 50, and such a force is not normally available.

The result is that as force F is applied to the door leaves 4, thedetent balls on the sides of the door leaves 4 nearest force F arereleased from their sockets before the detent balls release on theopposite sides of the door leaves. Once one of a pair of detents isreleased, the horizontal force at the other detent is reduced so that itcannot be released (unless the nut 77 is loosened, which would be donewhen the leaves are to be removed from the door). The same result occursat both the upper and lower collapsing mechanisms. With the upper andlower detents on the side of the door leaf away from force F remainingin contact with their ball sockets, such detents form pivot points aboutwhich the door leaf 4 continues to rotate as force F continues to beapplied.

In FIG. 11, door leaves 4a, 4b have been pivoted about the detentsfarthest away from force F while the detents closest to force F havebeen released. FIG. 12 shows door leaves 4a, 4b pivoted to the pointwhere the edges of the door leaves farthest away from central shaft 6have come into contact with door leaves 40, 4d. At this point force F istransmitted through door leaves 4a, 4b to door leaves 40, 4d.

In a similar manner to above the detents of door leaves 4c, 4d closestto force F are released and door leaves 4c, 4d are pivoted until thefour leaves eventually assume the position shown in FIG. 13, in whichthe door is book folded".

In order to return the door leaves to their uncollapsed position, theleaves are simply pivoted in the reverse direction by a force in adirection opposite to force F. As the detent balls 38 contact therun-outs 56 of the ball sockets 50, the balls 38 are depressed andtravel up the run-outs 56 until the balls seat in the spherical recesses52. The run-outs 56 and the recesses 52 provide a distinctive feel foran operator as balls 38 seat in order to reduce the likelihood that theleaves will be moved too far (i.e. overshoot).

The upper and lower edges of each door leaf 4 are provided with channels88 which hold conventional sealing strips 90. The sealing strips 90' inthe upper leaf channels extend up to sweep the surface 65a of theceiling 12, and the ring 66' while the sealing strips 90 in the lowerleaf channels sweep the floor 16 and the ring 66.

It will be noted that the outer arcuate edges of the bearing plates 28extend radially outwardly beyond the ball holders 36, thereby protectingthe ball holders against entry of dirt, and also hiding them, thusimproving the appearance of the door.

It will be seen that when the leaves are book folded as shown in FIG.13, the outer door leaves 4a, 4b have moved over the bearing plates 28c,28d of the inner leaves 4c, 4d. To allow this, the sealing strips 90,90' are of quite flexible material so that they can be pushed aside bythe bearing plates when the leaves are book folded.

It will be appreciated that various modifications may be made in thestructure described. For example, four door leaves have been shown sincethis number is conventional, but this number may be reduced to three,with the number of detents positioned in the retaining plates alsoreduced to six instead of eight.

If desired, the ball holders 36 and ball sockets 50 can be repositionedfrom the locations shown in the drawings, e.g. by being moved radiallyoutwardly and farther apart (by increasing the size of retaining plate18 and bearing plate 28). It should be noted, however, that when thedoor leaves pivot about one upper and lower set of detents, the outeredges of the door leaves swing out radially from the central verticaldoor axis. If the centre to centre distance between each of a pair ofdetents is too great, the outer edges of the door leaves may interferewith the shell 3 (FIG. 1) which encircles the door. Therefore, a typicalcentre to centre distance between a pair of detents would beapproximately 2% inches. A typical diameter of the pitch circle on aretaining plate 18 around which the detents are located would beapproximately 6 inches. Although interference between the outer edges ofthe door leaves and the encircling shell is a typical application willnot occur until the centre to centre distance between detents exceedsapproximately 10 inches, nevertheless, it is desirable to keep thefolding mechanism small to improve the appearance of the door. Thus, theinterference problem will not normally arise in practice.

The detents will normally be positioned equidistant from and on oppositesides of the plane of their associated door leaf, on a line taken atright angles to the plane of the door leaf. (The term plane ofa doorleaf as used in this description and in the appended claims means thevertical plane taken through the centre of the door leaf midway betweenthe faces of the door leaf.) The detents associated with a door leafcould if desired be positioned unequal distances from the plane of theirdoor leaf, or on a line not at right angles to the door leaf, but thepath of travel of the leaves when folded would then differ dependingwhich way they are folded. This is usually undesirable, and thereforeany departure from the detent positioning described will normally beeither zero or small.

It will further be appreciated that other detent mechanisms may be usedif desired, in place of (and in the location of) ball holders 36 andball sockets 50, to retain the door leaves in an extended position andto permit them to collapse upon application ofa force greater than apredetermined force. However, the detent mechanism illustrated anddescribed is believed to be the best embodiment in view of itseffectiveness and simplicity.

Further, the ball holders 36 and the ball sockets 50 can be interchangedin position so that the ball holders 36 are mounted on the bearingplates 28 and the ball sockets 50 are mounted on the retaining plates18. This embodiment would function in the same manner as the preferredembodiment but the elongated ball holder housings 40 would then have tobe buried in the leaves, which is less desirable than the arrangementshown. Alternatively, if desired, the ball sockets 50 can be formedintegrally with the bearing plates 28 (or with the retaining plates 18).

The upper portion of the door need not be made as strongly as the lowerportion of the door since the upper portion does not support the weightof the door as does the lower portion. In addition, although thebearings 64 are shown as supporting the door shaft through the retainingplate 18, the bearings 64 could if desired support and locate the shaft6 directly and not through retaining plate 18. However, in thearrangement shown, the retaining plate serves dual duty, not onlyretaining the ball holders 50 but also providing a flange for the thrustbearings 64, thus reducing cost.

Finally, if desired the central shaft 6 can be eliminated and the lowerand upper retaining plates 18, 18' can simply be rotatably secured tothe floor and ceiling respectively for rotation about the centralvertical axis formerly occupied by the shaft 6. The remainder of themechanism will be unchanged, except that the weather seals at the inneredges of the leaves will be extended to block air flow through thecentre of the door. Any desired means can be provided to adjust thevertical position of the upper or lower retaining plate, to adjust theforce with which the leaves are clamped between the retaining plates.

What I claim is:

I. In a collapsible revolving door having a central vertical axis and aplurality of door leaves, an improved mechanism for normally holdingsaid leaves in radially extended positions for rotation in unison aboutsaid axis with the inner edges of said leaves facing said axis, and forallowing collapsing of said leaves, said mechanism comprising:

a. upper and lower retaining plates concentric with said axis,

b. means mounting said upper retaining plate at the top of said door andsaid lower retaining plate at the bottom of said door for rotation ofsaid upper and lower retaining plates about said axis,

0. a plurality of bearing plates, one secured to the top and one to thebottom of each leaf adjacent the inner edges of said leaves, eachbearing plate projecting laterally to each side of the plane of its associated leaf, said bearing plates at the tops of said leaves facing andbeing spaced just below said upper retaining plate and said bearingplates at the bottom of said leaves facing and being spaced just abovesaid lower retaining plate,

(1. two detents coupled between each bearing plate,

and the retaining plate associated with such bearing plate, said detentsfor each bearing plate being located substantially equidistant from theplane of the door leaf associated with such bearing plate and on ahorizontal line substantially at right angles to such plane,

. said detents each including pivot means supporting their associatedleaf in normally fixed relation to said retaining plates and beingseparable upon application of a predetermined force applied thereto in afirst direction directed substantially radially away from said centralaxis through such pivot means and requiring a substantially higher forcein any direction other than said first direction for separation, so thatwhen a door leaf is pushed with a force sufficient to generate at thedetents at one side of the leaf a force in said first direction whichexceeds said predetermined force, said pivot means at the top and bottomof said one side of such leaf will separate allowing such leaf to pivotand fold about the pivot means at the top and bottom of the other sideof such leaf.

2. Apparatus according to claim 1 wherein each said detent comprises aball housing, a ball retained in and movable in said housing, and biasedto a position projecting from said housing, and a ball socket containinga shallow depression therein to seat said ball when said leaves are intheir normal radially extended position, said socket including a run-outextending from said depression substantially radially towards saidcentral axis when said leaves are in their normal radially extendedposition.

3. Apparatus according to claim 2 wherein said ball housings are locatedin said retaining plates and said sockets are located in said bearingplates.

4. Apparatus according to claim 1 wherein said door has a centralrotatable vertical shaft aligned with said axis, said upper and lowerretaining plates being concentric with said shaft and secured to saidshaft adjacent the top and bottom of said shaft respectively.

5. Apparatus according to claim 2 wherein said ball housings are locatedin said retaining plates and said sockets are located in said bearingplates.

6. Apparatus according to claim 5 wherein said sockets are each discretemembers removable from their bearing plates.

7. Apparatus according to claim 4 including a pair of main housings forsaid shaft, one at the bottom and one at the top of said shaft, andretaining plates being located in said main housings and said ballhousings extending into said main housings.

8. Apparatus according to claim 7 wherein the centres of said detentsare spaced about 2% inches apart.

9. Apparatus according to claim 4 wherein said shaft includes upper andlower shaft portions, said upper retaining plate being secured to saidupper shaft portion and said lower retaining plate being secured to saidlower shaft portion, and means coupled to said upper and lower shaftportions for drawing said upper and lower shaft portions together, tosecure said leaves between said retaining plates.

1. In a collapsible revolving door having a central vertical axis and aplurality of door leaves, an improved mechanism for normally holdingsaid leaves in radially extended positions for rotation in unison aboutsaid axis with the inner edges of said leaves facing said axis, and forallowing collapsing of said leaves, said mechanism comprising: a. upperand lower retaining plates concentric with said axis, b. means mountingsaid upper retaining plate at the top of said door and said lowerretaining plate at the bottom of said door for rotation of saId upperand lower retaining plates about said axis, c. a plurality of bearingplates, one secured to the top and one to the bottom of each leafadjacent the inner edges of said leaves, each bearing plate projectinglaterally to each side of the plane of its associated leaf, said bearingplates at the tops of said leaves facing and being spaced just belowsaid upper retaining plate and said bearing plates at the bottom of saidleaves facing and being spaced just above said lower retaining plate, d.two detents coupled between each bearing plate, and the retaining plateassociated with such bearing plate, said detents for each bearing platebeing located substantially equidistant from the plane of the door leafassociated with such bearing plate and on a horizontal linesubstantially at right angles to such plane, e. said detents eachincluding pivot means supporting their associated leaf in normally fixedrelation to said retaining plates and being separable upon applicationof a predetermined force applied thereto in a first direction directedsubstantially radially away from said central axis through such pivotmeans and requiring a substantially higher force in any direction otherthan said first direction for separation, so that when a door leaf ispushed with a force sufficient to generate at the detents at one side ofthe leaf a force in said first direction which exceeds saidpredetermined force, said pivot means at the top and bottom of said oneside of such leaf will separate allowing such leaf to pivot and foldabout the pivot means at the top and bottom of the other side of suchleaf.
 2. Apparatus according to claim 1 wherein each said detentcomprises a ball housing, a ball retained in and movable in saidhousing, and biased to a position projecting from said housing, and aball socket containing a shallow depression therein to seat said ballwhen said leaves are in their normal radially extended position, saidsocket including a run-out extending from said depression substantiallyradially towards said central axis when said leaves are in their normalradially extended position.
 3. Apparatus according to claim 2 whereinsaid ball housings are located in said retaining plates and said socketsare located in said bearing plates.
 4. Apparatus according to claim 1wherein said door has a central rotatable vertical shaft aligned withsaid axis, said upper and lower retaining plates being concentric withsaid shaft and secured to said shaft adjacent the top and bottom of saidshaft respectively.
 5. Apparatus according to claim 2 wherein said ballhousings are located in said retaining plates and said sockets arelocated in said bearing plates.
 6. Apparatus according to claim 5wherein said sockets are each discrete members removable from theirbearing plates.
 7. Apparatus according to claim 4 including a pair ofmain housings for said shaft, one at the bottom and one at the top ofsaid shaft, and retaining plates being located in said main housings andsaid ball housings extending into said main housings.
 8. Apparatusaccording to claim 7 wherein the centres of said detents are spacedabout 2 3/4 inches apart.
 9. Apparatus according to claim 4 wherein saidshaft includes upper and lower shaft portions, said upper retainingplate being secured to said upper shaft portion and said lower retainingplate being secured to said lower shaft portion, and means coupled tosaid upper and lower shaft portions for drawing said upper and lowershaft portions together, to secure said leaves between said retainingplates.